This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鑡 combines 金 (metal) with 齒 (teeth). The exact historical development is uncertain, but it likely relates to a metal object associated with teeth or a large plate.
Metal 金 and teeth 齒 together suggest a metal plate or object related to teeth, but the exact meaning is unclear.
For サク, imagine a sack of metal teeth: sack -> サク, and the metal teeth clatter inside.